The present invention relates to an apparatus for monitoring the yarn being removed from an open-end spinning turbine whose rotor is mounted in the machine in an elastically mounted bearing and in which there is associated with the rotor and/or the bearing at least one sensor which responds to radial deflections of its associated part and whose signals are fed to an evaluation circuit to generate a signal, as disclosed in a copending application entitled APPARATUS FOR MONITORING THE YARN PRODUCED BY AN OPEN-END SPINNING TURBINE, filed by Heinz Wehde on about the same date as the present application and claiming priority of German Application P 26 57 525.7 of Dec. 18th, 1976.
The invention disclosed therein is based on the fact that even limited deposits of dirt in the rotor of an open-end spinning turbine give rise to an imbalance. With an elastically mounted rotor, or a rotor which is mounted so as to elastically align its geometrical axis with the axis of inertia, respectively, the rotor rotates supercritically about its major axis of inertia. If the rotor possesses an imbalance, this axis of inertia no longer coincides with the rest position of the rotor axis; rather this axis traces a conical or cylindrical path which is concentric with the rotor axis rest position. Projected onto a plane through the axis rest position, the movements of the axis and of the bearing have the form of oscillations which can be measured with known sensors. The amplitude of these oscillations depends on the extent, or magnitude, of the imbalance.
By selecting a threshold value for those signals generated by the oscillations which will be processed, the signals created by dirt deposits can be extracted from the complete signal stream.
As already indicated, the bearing or rotor oscillation amplitude can be used as a measuring criterion. Another possibility is to sense the oscillation velocity, or rate of change of position of the bearing, which is of course also dependent on the oscillation amplitude, this representing another way of distinguishing between signal values having different causes.
With this imbalance measurement according to the pending application, the yarn is monitored with respect to irregularities. If a number of irregularities occur per unit time at regular intervals, this can be evaluated as an indication that a moire effect will be present in fabric produced from the yarn. However, thickened portions occurring at irregular intervals can also be detected and prevented.